High-frequency Induction Heated Sintering Research Articles

High-Frequency Induction Heat Sintering of Al2O3/Al7075 Composites.

High-Frequency Induction Heat Sintering of Al2O3/Al7075 Composites.

Effect of Synthesized Titanium Dioxide Nanofibers Weight Fraction on the Tribological Characteristics of Magnesium Nanocomposites Used in Biomedical Applications.

Biomedical applications, such as artificial implants, are very significant for the disabled due to their usage in orthopedics. Nevertheless, available materials in such applications have insufficient mechanical and tribological properties. The current study investigated the mechanical and tribological properties of a biomedical metallic material, magnesium (Mg), after incorporating titanium dioxide nanofibers (TiO2) with different loading fractions. The TiO2 nanofibers were synthesized using the electrospinning technique. The ball-milling technique was utilized to ensure the homogenous distribution of TiO2 nanofibers inside the Mg matrix. Then, samples of the mixed powder with different loading fractions of TiO2 nanofibers, 0, 1, 3, 5, and 10 wt.%, were fabricated using a high-frequency induction heat sintering technique. The physicomechanical and tribological properties of the produced Mg/TiO2 nanocomposites were evaluated experimentally. Results showed an enhancement in mechanical properties and wear resistance accompanied by an increase in the weight fraction of TiO2 nanofibers up to 5%. A finite element model was built to assess the load-carrying capacity of the Mg/TiO2 composite to estimate different contact stresses during the frictional process. The finite element results showed an agreement with the experimental results.

Evaluation of high-frequency induction heat sintering and conventional sintering in AlxCoCrFeMnNi high-entropy alloys

AlxCoCrFeMnNi high-entropy alloys with different aluminum concentrations (x = 0.5, 1, and 1.5 at%) were synthesized by mechanical alloying followed by consolidation using two different sintering methods, conventional (CS) and high-frequency induction heat + conventional (HFIHS + CS). The results show the presence of FCC, BCC, and B2ordered phases in all systems, regardless of the sintering method. The BCC phase exhibits morphological changes (cuboidal-type and plate-like) associated with the two sintering methods involving different diffusion rates and affecting the hardness values. The M23C6 carbide is identified in systems sintered by the CS method; meanwhile, the M7C3 carbide is identified in the HFIHS + CS method. Finally, the HFIHS + CS method results in a higher level of densification (~95%) than the CS method (~80%).

The Effect of Ball Milling on Properties and Sintering of Nanostructured TiB₂.

TiB₂ powder was milled in a high-energy ball mill (Pulverisette-5 planetary mill) at 250 rpm for various time periods (0, 1, 4, and 10 h) and consolidated by the high frequency induction heated sintering (HFIHS). The effect of milling on the sintering behavior and crystallite size of TiB₂ powders were investigated. A nanostructured dense TiB₂ specimen with a relative density of up to 98% was readily achieved within very short time (two min). The ball milling effectively refined the crystallite structure of TiB₂ powders and facilitated the subsequent consolidation. The sinter-onset temperature was reduced remarkably by the prior milling for 10 h. Accordingly, the relative density and mechanical properties of TiB₂ compact increased as the milling time increased.

Mechanical Properties and Rapid Sintering of Nanostructured WC-Al₂O₃-Al Hard Materials.

Nanostructured WC-Al₂O₃-Al composites was sintered using rapid high-frequency induction heated sintering (HFIHS) and the mechanical properties such as hardness and fracture toughness with consolidation were investigated. The HFIHS method induced a very fast densification nearly at the level of theoretical density and successfully prohibited grain growth, resulting in nano-sized grains. The fracture toughness was improved due to the consolidation facilitated by adding Al to WC-Al₂O₃ matrix. The WC-Al₂O₃ composites added with 5 and 10 vol.% Al showed higher hardness and fracture toughness compared with that of WC-Al₂O₃.

Balanced Mechanical and Tribological Performance of High-Frequency-Sintered Al-SiC Achieved via Innovative Milling Route—Experimental and Theoretical Study

In this study, Al-SiC nanocomposite was fabricated via powder metallurgy route using different innovative high-energy ball-milling techniques (HEBM). The powder mixture was consolidated using high-frequency induction heat sintering process (HFIHS). With the aim of studying the physical, mechanical, and tribological performance of the fabricated nanocomposites. Relative density, hardness, compressive yield strength, Young’s modulus, toughness, elongation, specific wear rate and coefficient of friction were experimentally investigated. A finite element model for the frictional process was built to find out the distribution of contact stresses as result of samples sliding. It was found that the highest the energy of the milling, the more improvement in the mechanical and tribological performance could significantly achieved due to the homogeneous distribution and the excellent bonding effect of the composite. In addition, field emission scanning electron microscope was used for studying the sliding surface morphology in order to explicate the mechanism of the dry wear process.

Effect of alloying elements on thermal stability of nanocrystalline Al alloys

Abstract The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated. Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated. The initial mixtures of powders were milled for 100 h in vacuum. The bulk samples were fabricated from the milled powders in a high frequency induction heat sintering (HFIHS) system. The milled powders and the bulk sintered samples were characterized by X-ray diffraction (XRD), Vickers microhardness, field emission scanning electron microscopy (FESEM-EDS) and transmission electron microscopy (TEM). The observations indicated that Fe and Ti were completely dispersed in the matrix to form a supersaturated solid solution (SSSS) with Al. Additionally, the inclusion of alloying elements led to an increase in hardness and yield strength of the alloy by 127% and 152%, respectively. The elevated temperature compression tests were carried out to evaluate the thermal stability of the alloys. The Al−10wt.%Fe−5wt.%Ti alloy revealed the optimum thermally stable behavior of the three alloys studied. The incorporation of Fe and Ti improved the thermal stability of the developed alloys through inhibiting the grain growth, hindering dissolution and growth of second phases (such as Al13Fe4 and Al13Ti), and forming a stable solid solution.

Characterization of hydroxyapatite-reduced graphene oxide nanocomposites consolidated via high frequency induction heat sintering method

ABSTRACT In this study, a solvothermal method at the temperature of 180 °C for 4 h was used for the synthesis of hydroxyapatite-reduced graphene oxide (HA-rGO) nanopowders by employing the nitrogen gas injection. To synthesize the powders, a solvent containing dimethylformamide, anhydrous ethanol, diethylene glycol, and water was used (1:1:1:2, respectively). Calcium nitrate tetrahydrate and diammonium hydrogenphosphate were used as calcium and phosphate precursors, respectively. The synthesized powders were consolidated by a high-frequency induction heat sintering method. The powders and sintered samples were then evaluated using X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, Vickers indentation technique, and biocompatibility assay. The findings of this study showed that the final powders synthesized by the solvothermal method had calcium to phosphate ratio of about 1.67. The high frequency induction heat sintering method was suitable for consolidating these powders and exhibited a higher relative density than other methods. The mechanical properties of the nanocomposite were higher than those of pure HA. In biological experiments the difference of HA effect in comparison with the nanocomposite was not significant and both were biocompatible.

Mechanical Properties and Rapid Sintering of WC-BN-Al Composites

Tungsten carbides are quite attractive for their superior properties, e.g., high melting point, high hardness, high thermal and electrical conductivities, and relatively high chemical stability. Tungsten carbides with a binder metal, for example Co or Ni, are mainly used to produce cutting tools, nozzles and molds in the composite form. But these binder materials show inferior chemical characteristics compared to the tungsten carbide phase. There has been enormous interest recently in finding alternative binder phases because of the low corrosion resistance and the high cost of Ni or Co. Al has been reported as an alternative binder for WC and TiC, since Al is less expensive and shows a higher oxidation resistance than Ni or Co. Nanostructured WC-BN-Al composites were rapidly sintered using high-frequency induction heated sintering (HFIHS). The microstructure and mechanical properties (fracture toughness and hardness) were investigated by Vickers hardness tester and FE-SEM. The HFIHS method induced very fast densification, nearly at the level of theoretical density, and successfully prohibited grain growth, resulting in nano-sized grains. The fracture toughness was improved by consolidation facilitated by adding Al to the WC-BN matrix. The 5vol % Al added WC-BN composites showed higher mechanical properties (hardness and fracture toughness than the WC-BN composite.

Mechanochemical Synthesis and Rapid Consolidation of Nanostructured Nb–ZrO2 Composite

Nb₂O5 and Zr powders at a molar ratio of 1:2.5 were milled using a high-energy ball mill. The mixture powders produced Nb and ZrO₂ nanopowders through a solid replacement reaction (Nb₂O5+ 2.5Zr 2Nb + 2.5ZrO₂). The synthesized nanopowders were consolidated via high-frequency induction heated sintering (HFIHS) within two min. The mechanical properties (hardness and fracture toughness) of nanostructured 2Nb-2.5ZrO₂ composite were then evaluated. Both the hardness and fracture toughness of the 2Nb-2.5ZrO₂ composite were higher than those of monolithic ZrO₂.

Evaluation of Argon-Gas-Injected Solvothermal Synthesis of Hydroxyapatite Crystals Followed by High-Frequency Induction Heat Sintering

In this study, the two-state solvothermal method (180 °C) was used for the synthesis of hydroxyapatite nanoparticles. The former is traditional (2, 4 h), and the latter, with argon gas injection (1...

Enhanced Thermoelectric Properties of WS2/Single-Walled Carbon Nanohorn Nanocomposites

Recently, two-dimensional tungsten disulfide (WS2) has attracted attention as a next generation thermoelectric material due to a favorable Seebeck coefficient. However, its thermoelectric efficiency still needs to be improved due to the intrinsically low electrical conductivity of WS2. In the present study, thermoelectric properties of WS2 hybridized with highly conductive single-walled carbon nanohorns (SWCNHs) were investigated. The WS2/SWCNH nanocomposites were fabricated by annealing the mixture of WS2 and SWCNHs using a high-frequency induction heated sintering (HFIHS) system. By adding SWCNHs to WS2, the nanocomposites exhibited increased electrical conductivity and a slightly decreased Seebeck coefficient with the content of SWCNHs. Hence, the maximum power factor of 128.41 μW/mK2 was achieved for WS2/SWCNHs with 0.1 wt.% SWCNHs at 780 K, resulting in a significantly improved thermoelectric figure of merit (zT) value of 0.027 compared to that of pristine WS2 with zT 0.017.

Mechanical and tribological characterization of nanostructured graphene sheets/A6061 composites fabricated by induction sintering and hot extrusion

An aluminum alloy (A6061) reinforced with graphene nanosheets (GNSs) was successfully fabricated by ultrasonic processing, high-frequency induction heat sintering (HFIHS), and hot extrusion. Harmful aluminum carbide (Al4C3) was not formed during HFIHS process as well as GNS particles were found to be able to stimulate recrystallization, restrict grain growth, and disturb the preferential texture in the present work. Enhancements in compressive strength of up to 50.4%, Vickers hardness of 13.3% as well as a 21.7% reduction in the friction coefficient along with a 17.2% reduction in the wear rate compared with those of as-extruded A6061 were measured. These improvements were due to the homogeneous dispersion of 0.25 wt% GNSs in the matrix. In addition, the yield strength predicted using modified model was in good agreement with the experimental results reported in this study. However, deterioration of the mechanical properties of the composites and a discrepancy between the theoretical prediction and experimental values occurred with the addition of 0.5 wt% GNSs owing to GNS agglomeration. This study demonstrated that the incorporation of an appropriate amount of GNSs can enhance the overall properties of a metal matrix, opening up an innovative design concept for fabricating bulk metal matrix composites (MMCs).

Ceramic nanofibers versus carbon nanofibers as a reinforcement for magnesium metal matrix to improve the mechanical properties

Light composite materials based on Magnesium matrix reinforced with carbon or ceramic nanofibers were fabricated by powder metallurgy rout using high frequency induction heat sintering (HFIHS) technique. A comprehensive comparative study has been investigated on using ceramic nanofibers and carbon nanofibers as a fibers reinforced Magnesium metal matrix in order to evaluate the overall improvements in mechanical properties. Electrospinning technique followed by calcination process were used efficaciously to synthesize and fabricate the Titanium Oxide (TiO2) fibers and carbon fibers. Mg/nanofibers mixtures were prepared via powder metallurgy route using mechanical alloying technique by adding 1, 3, 5 and 10 wt% calcined nanofibers to Mg matrix. In inert atmosphere and room temperature, mixtures were initially processed using high energy ball milling for 15 + 15 min. The final bulk cylindrical samples were obtained by performing consolidation or sintering process using high frequency induction heat sintering furnace (HFIHS). Characterization of the sintered composites have been investigated using field emission scanning electron microscopes (FESEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). While, hardness test and compression test were performed in order to evaluate the mechanical properties of the fabricated composites. The obtained result shows that, the ultimate compressive strength increased to 281 MPa at 5 wt% TiO2, which represent about 12.4% more than the pure Mg. Hardness improved up to 64.4% in case of using the ceramic nanofibers as reinforcement. While using CNFs as reinforcement to the Mg matrix, slightly deteriorates the mechanical properties.

Transient Liquid Phase Bonding of Ti-6Al-4V and Mg-AZ31 Alloys Using Zn Coatings.

Ti-6Al-4V and Mg-AZ31 were bonded together using the Transient Liquid Phase Bonding Process (TLP) after coating both surfaces with zinc. The zinc coatings were applied using the screen printing process of zinc paste. Successful bonds were obtained in a vacuum furnace at 500 °C and under a uniaxial pressure of 1 MPa using high frequency induction heat sintering furnace (HFIHS). Various bonding times were selected and all gave solid joints. The bonds were successfully achieved at 5, 10, 15, 20, 25, and 30 min. The energy dispersive spectroscopy (EDS) line scan confirmed the diffusion of Zn in both sides but with more diffusion in the Mg side. Diffusion of Mg into the joint region was detected with significant amounts at bonds made for 20 min and above, which indicate that the isothermal solidification was achieved. In addition, Ti and Al from the base alloys were diffused into the joint region. Based on microstructural analysis, the joint mechanism was attributed to the formation of solidified mixture of Mg and Zn at the joint region with a presence of diffused Ti and Al. This conclusion was also supported by structural analysis of the fractured surfaces as well as the analysis across the joint region. The fractured surfaces were analyzed and it was concluded that the fractures occurred within the joint region where ductile fractures were observed. The strength of the joint was evaluated by shear test and found that the maximum shear strength achieved was 30.5 MPa for the bond made at 20 min.

Thermal stability of nanocrystalline Al−10Fe−5Cr bulk alloy

Abstract Thermal stability of nanocrystalline Al−10wt.%Fe−5wt.%Cr bulk alloy was investigated. The initial micro-grained mixture of powders was processed for 100 h using mechanical alloying (MA) to produce nano-grained alloy. The processed powders were sintered using high frequency induction heat sintering (HFIHS). The microstructures of the processed alloy in the form of powders and bulk samples were investigated using XRD, FESEM and HRTEM. Microhardness and compression tests were conducted on the bulk samples for evaluating their mechanical properties. To evaluate the thermal stability of the bulk samples, they were experimented at 573, 623, 673 and 723 K under compression load at strain rates of 1×10−1 and 1×10−2 s−1. The annealed samples exhibited a significant increase in their microhardness value of 2.65 GPa when being annealed at 723 K, as compared to 2.25 GPa of the as-sintered alloy. The bulk alloy revealed compressive strengths of 520 MPa and 450 MPa at 300 K and 723 K, respectively, when applying a strain rate of 1×10−1 s−1. The microstructural stability of the bulk alloy was ascribed to the formation of iron and chromium containing phases with Al such as Al6Fe, Al13Fe4 and Al13Cr2, in addition to the supersaturated solid solution (SSSS) of Cr and Fe in Al matrix.

Microstructural Evaluation of Inductively Sintered Aluminum Matrix Nanocomposites Reinforced with Silicon Carbide and/or Graphene Nanoplatelets for Tribological Applications

Silicon carbide (SiC) nanoparticles (NP) and/or graphene nanoplatelets (GNP) were incorporated into the aluminum matrix through colloidal dispersion and mixing of the powders, followed by consolidation using a high-frequency induction heat sintering process. All the nanocomposite samples exhibited high densification (> 96 pct) with a maximum increase in Vickers microhardness by 92 pct relative to that of pure aluminum. The tribological properties of the samples were determined at the normal frictional forces of 10 and 50 N. At relatively low load of 10 N, the adhesive wear was found to be the predominant wear mechanism, whereas in the case of a 50 N normal load, there was significant contribution from abrasive wear possibly by hard SiC NP. From wear tests, the values for the coefficient of friction (COF) and the normalized wear rate were determined. The improvement in hardness and wear resistance may be attributed to multiple factors, including high relative density, uniform SiC and GNP dispersion in the aluminum matrix, grain refinement through GNP pinning, as well as inhibition of dislocation movement by SiC NP. The nanocomposite sample containing 10 SiC and 0.5 GNP (by wt pct) yielded the maximum wear resistance at 10 N normal load. Microstructural characterization of the nanocomposite surfaces and wear debris was performed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The synergistic effect of the GNP and SiC nanostructures accounts for superior wear resistance in the aluminum matrix nanocomposites.

Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

Toughness enhancement in graphene nanoplatelet/SiC reinforced Al2O3 ceramic hybrid nanocomposites

This paper elucidates the effect of silicon carbide nanoparticles (SiCNP) and graphene nanoplatelets (GNPs), on their own and together, on the densification behavior and fracture toughness of alumina (Al2O3) ceramic matrix. This was investigated by using the high-frequency induction heat sintering (HFIHS) process. While the addition of each nanostructure caused varying degrees of grain refinement and enhancement of mechanical properties, the incorporation of as little as 0.5 wt.% GNPs along with 5.0 wt.% SiCNP promoted uniform dispersion of the latter due to the lateral surface area of the graphene nanosheets with their two-dimensional morphology. There was an associated reduction in grain size from 1500 to 300 nm upon the addition of both types of nanoscale reinforcements. Extensive electron microscopy of the as-produced nanocomposites indicated the presence of SiCNP within, as well as at, the grain boundary areas whereas the 2D GNPs anchored between neighboring grains. Fractography of the samples revealed a transition from a mixed intergranular/transgranular mode for SiCNP or GNP-reinforced nanocomposites to transgranular fracture mode for the hybrid nanocomposites with improvements in fracture toughness and microhardness by 160 and 27%, respectively, largely due to the synergic role of the nanostructured reinforcements and their distinctly different toughening mechanisms. A new toughening model is proposed for the hybrid nanocomposites by taking into consideration crack deflection and pull-out effects due to SiCNP and the atomic level slip-stick driven GNPs inter-layer slithering. It was found that the addition of GNPs facilitates SiCNP dispersion that subsequently develops dense, fine-grained microstructures after a short-cycle, pressure-assisted consolidation process.

Processing and Thermal Properties of Multiwall Carbon Nanotube/Bismuth Antimony Telluride Composites for Nuclear Energy Applications

In this work the effects of ball milling and carbon nanotubes incorporation on the thermal conductivities of the bulk BiSbTe composites were evaluated. The coarse BiSbTe particles were obtained by crushing BiSbTe lumps and subsequently high energy ball milling was employed in an inert environment to form the fine BiSbTe powder. Multiwall carbon nanotubes in different (0.0, 0.5 and 1.5) vol. % were uniformly mixed in the BiSbTe powder through a combination of ultra-sonication and ball milling, and then processed by rapid high frequency induction heated sintering (HFIHS) to achieve fully dense nanocomposite. Thermal diffusivity of the composites was evaluated and heat capacity was approximated using Pyrocerarm as a reference material. The effect of carbon nanotubes inclusion and BiSbTe particle size reduction on the thermal conductivity was studied from 300 to 500 K. The results show a significant reduction in the thermal conductivity due to the enhanced thermal boundary interface resistance correlated with the fine microstructure/nanostructure in the composites as compared to pristine bulk bismuth antimony telluride.